This invention relates to a sliding door, and more particularly to a sliding door for air-tightly closing an entrance of a large-sized freezer, a large-sized refrigerator, a freezing storehouse, a refrigerating storehouse, a clean room or the like which is used for business purpose.
In general, such a sliding door is large-sized and formed into increased thickness and weight due to its heat insulating structure. Also, the conventional sliding door is so constructed that a packing arranged on a periphery of a door body is elastically closely contacted with a periphery of an entrance and a floor of a large-sized freezer or the like in order to provide the freezer with air-tightness when the entrance is closed with the door. Unfortunately, such construction causes much labor to be required at the initial stage of a door opening operation.
More particularly, for example, the conventional sliding door, as shown in FIGS. 4A and 4B, is so constructed that a wheel 2 rotatably mounted on each of brackets B fixed on an upper portion of a door body 1 is carried on a guide rail 5 horizontally arranged above an entrance 4 of an object to be operated with the sliding door such as a freezing storehouse or the like. The door body 1 is provided on a periphery of an inner surface thereof with a packing 6 and on a bottom thereof with a bottom packing 7. The guide rail 5 is formed at a portion thereof positionally corresponding to the entrance 4 with two sets of combinations each comprising an inward inclined portion 8 and a downward inclined portion 9.
In the above-described construction of the conventional sliding door, when the door body 1 reaches the entrance 4, the wheels 2 carried on the guide rail 5 are inward moved while being guided along the inward inclined portions 8, so that the peripheral packing 6 is pressed onto the periphery of the entrance 4. Concurrently, the wheels 2 are moved to the downward inclined portions 9 to cause the door body 1 to be lowered, resulting in the bottom packing 7 being pressedly contacted with the floor 3. Thus, the entrance 4 is air-tightly closed with the sliding door.
Unfortunately, the conventional sliding door 1 is large-sized and formed into weight as much as several tens of kilograms. Therefore, in order to open the door closed once, it is required to put out the wheels 2 from the downward inclined portions 9 against frictional resistance between the bottom packing 7 and the floor 3 while pushing up the weighty door. Concurrently, it is required to separate the peripheral packing 6 from the periphery of the entrance 4 against frictional resistance therebetween. Thus, starting of the door opening operation requires much labor.
Further, motorization of a sliding door recently takes place. However, in the conventional sliding door, as described above, much labor is required at the initial stage of the door opening operation, so that the motorization requires a motor of a large capacity. Thus, it causes problems such as an increase in manufacturing cost, an increase in operating cost, an increase in installation space and the like.